The trend in the design of parafoil wing sections is toward higher lift-to-drag ratios which afford greater glide distances. Self-inflating parafoils are known in which the leading edge of the foil is provided with ram-air induction vents through which air inflates the foil during flight with a positive air pressure.
One such inflatable parafoil is disclosed in U.S. Pat. No. 4,860,970 in which orifices along the leading edge of the foil admit inflating air into a tubular plenum extending across the span of the foil. Air is directed through the tubular plenum toward the tips of the foil and out through apertures in the trailing edge of the foil.
U.S. Pat. No. 4,424,945 discloses a flexible parafoil to which is suspended a rigid wing and frame. The parafoil is divided into several sections which are open at the front or leading edges thereof to collect air in the manner of a ram air scoop. Other forms of ram air-inflated gliding parachutes are disclosed in U.S. Pat. Nos. 4,065,079 and 4,865,274.
While the foregoing conventional parafoil designs advantageously provide a positive air pressure for self-inflation of the parafoil wing section, there is a significant drawback to these designs. The ram air openings or orifices on the leading edge of the parafoils substantially increase the drag coefficient of the foil. Consequently, the lift-to-drag ratio of the foil is reduced thereby offsetting to some extent the advantage of a greater glide distance for a wing section with a high lift-to-drag ratio.
It would be desirable therefore to provide a self-inflating parawing design that increases drag only minimally, if at all, and still maintains a high lift-to-drag ratio. It would also be desirable to increase the span-to-chord ratio of the parawing to further increase its lift-to-drag ratio.